Add configure option to disable scanner compilation

When cross-compiling Wayland, wayland-scanner should be picked up from
the host system instead of compiling and trying to run e.g. ARM
wayland-scanner on X86.

This patch adds --disable-scanner option for disabling the scanner
from the build and using existing wayland-scanner instead (from PATH)
which should help in most cross-compilation systems.

By default everything works as before.

Signed-off-by: Jani Uusi-Rantala <jani.uusi-rantala@nokia.com>

configure.ac

@@ -27,6 +27,14 @@ if test "x$GCC" = "xyes"; then
 fi
 AC_SUBST(GCC_CFLAGS)
 
+AC_ARG_ENABLE([scanner],
+              [AC_HELP_STRING([--disable-scanner],
+                              [Disable compilation of wayland-scannner])],
+              [],
+              [enable_scanner=yes])
+
+AM_CONDITIONAL(ENABLE_SCANNER, test "x$enable_scanner" = xyes)
+
 EXPAT_LIB=""
 AC_ARG_WITH(expat, [  --with-expat=<dir>      Use expat from here],
 		   [ expat=$withval

wayland/Makefile.am

@@ -35,9 +35,16 @@ AM_CPPFLAGS = $(FFI_CFLAGS)
 AM_CFLAGS = $(GCC_CFLAGS)
 
 protocoldir = $(top_srcdir)/protocol
+
+if ENABLE_SCANNER
 wayland_scanner = $(top_builddir)/wayland/wayland-scanner
+else
+wayland_scanner = wayland-scanner
+endif
+
 include $(top_srcdir)/wayland/scanner.mk
 
+if ENABLE_SCANNER
 bin_PROGRAMS = wayland-scanner
 
 wayland_scanner_SOURCES =				\
@@ -46,6 +53,7 @@ wayland_scanner_SOURCES =				\
 wayland_scanner_LDADD = $(EXPAT_LIBS) libwayland-util.la
 
 $(BUILT_SOURCES) : wayland-scanner
+endif
 
 BUILT_SOURCES =					\
 	wayland-server-protocol.h		\